See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/227861380
Heat sealability of laminated films with LLDPE and LDPE as the sealant materials
in bar sealing application
Article in Journal of Applied Polymer Science · June 2007
DOI: 10.1002/app.25863
CITATIONS
READS
39
11,899
4 authors:
See Yuan Cheng
Azman Hassan
Technical University of Malaysia Malacca
Universiti Teknologi Malaysia
28 PUBLICATIONS 178 CITATIONS
312 PUBLICATIONS 5,685 CITATIONS
SEE PROFILE
SEE PROFILE
Mohd Imran Ghazali
Ahmad Fauzi Ismail
Universiti Tun Hussein Onn Malaysia
Universiti Teknologi Malaysia
49 PUBLICATIONS 413 CITATIONS
1,194 PUBLICATIONS 25,911 CITATIONS
SEE PROFILE
Some of the authors of this publication are also working on these related projects:
BN based Lamellar Membrane View project
fabrication dual layer hollow fiber membrane View project
All content following this page was uploaded by See Yuan Cheng on 13 July 2018.
The user has requested enhancement of the downloaded file.
SEE PROFILE
Heat Sealability of Laminated Films with LLDPE and
LDPE as the sealant Materials in Bar Sealing Application
Cheng See Yuan,1 Azman Hassan,2 Mohd Imran Hj Ghazali,3 Ahmad Fauzi Ismail4
1
Department of Thermal-Fluid, Faculty of Mechanical Engineering, Kolej Universiti Teknikal Kebangsaan Malaysia,
75450 Ayer Keroh, Melaka, Malaysia
2
Department of Polymer Engineering, Universiti Teknologi Malysia, Skudai, Malaysia
3
Department of Mechanical Engineering, Kolej Universiti Teknologi Tun Hussein Onn, Johor, Malaysia
4
Department of Gas Engineering, Universiti Teknologi Malysia, Skudai, Malaysia
Received 22 June 2006; accepted 9 November 2006
DOI 10.1002/app.25863
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The heat sealability of laminated films with
linear low density polyethylene (LLDPE) and low density
polyethylene (LDPE) as the sealant materials was investigated. A laboratory heat sealer was used to study the
response of laminated films to temperature, time, and pressure. Platen temperature was confirmed as primary factor
in controlling heat-seal strength. Dwell time must be sufficiently long to bring the interfacial temperature to a desired
level. When the desired heat-seal strength has been
achieved, further increase of dwell time did not improved
heat-seal strength. Platen pressure had little effect above the
level required to flatten the materials for good contact. Bar
sealing process window for each sample were developed.
The optimum combination of platen temperature and dwell
time for each laminated film can be obtained in the respec-
INTRODUCTION
Bar sealing is the most widely used method to produce a seal in most form/fill/seal machines.1 There
are three parameters in heat-sealing process, namely
the sealing temperature, dwell time, and sealing
pressure. Good seal will only be produced if these
three parameters are in proper combination when
forming a seal.
In heat-sealing process, heat is applied to melt the
sealing layer to a molten stage, or partially molten to
effect sealing. The acceptable temperature for heatsealing process is not a single temperature setting as
the plastic can be sealed at partially molten, or a
completely melt conditions. Therefore, the acceptable
sealing temperature is a range of temperature setting
in which a good seal will be produced for as long as
it is being made within this temperature range.
Dwell time is the duration of time that the laminated
film is brought into intimate contact by the heated
Correspondence to: A. Hassan (azmanh@fkkksa.utm.my).
Journal of Applied Polymer Science, Vol. 104, 3736–3745 (2007)
C 2007 Wiley Periodicals, Inc.
V
tive process windows. Strength of heat-seal and its failure
modes are closely related. Plateau initiation temperature
closely corresponds to the final melting point of sealant
materials. Relatively higher platen temperature was
required to seal laminated films with lower thermal conductance. Required dwell time corresponds closely to the
heat flow rate of bar sealing process. Laminated films made
from extrusion lamination process provided lower level of
achievable heat seal strength when compared with the laminated films made from dry-bond lamination process. Ó 2007
Wiley Periodicals, Inc. J Appl Polym Sci 104: 3736–3745, 2007
Key words: heat-sealing; linear low density polyethylene
(LLDPE) film; low density polyethylene (LDPE) film; seal
strength; process window
bars during the heat-seal cycle. The optimum dwell
time setting is important to ensure enough heat is
applied to the sealant material, and no excessive
time is wasted which may reduced the production
speed. The greater the heat flow rate, the shorter the
dwell time required. Thus, heat flow rate is a significant variable which determine the dwell time of the
process. During heat-sealing process, the heated portions of the packaging material (thermoplastic) needs
to be held together so that the molten plastic will
not skid and resulting in a bad seal, wrinkle in seal,
or corner leak. Thus, it is crucial that pressure is
exerted continuously at right angle to the direction
of the planes of the dies to press the heated packaging materials together throughout the entire heating
cycle.
Obviously, a container made of a multilayer flexible-packaging material (laminated film) can be no
stronger than the seal that holds it together.1 Therefore, acceptable heat-seal can be defined as a seal
which has its strength greater than the strength of the
packaging material. This corresponds to the delaminating or tearing mode failure in the peel test specimen, where the laminated film was failed rather than
the heat-seal fail in a peeling mode failure.
HEAT SEALABILITY OF LAMINATED FILMS WITH LLDPE, LDPE
If this requirement is not fulfilled, heat-seal of a
package will break open before the laminated film.
Consequently, this would be a waste of using strong
laminated film which is usually more expansive, as
the package can easily be failed at the seal when
subjected to loads.
Several studies concerning heat-sealing parameters
and the characteristics of the sealant material have
been reported in literature. Theller2 was the pioneer
researcher of this technique. He studied the heat
sealability of plastic film in bar sealing applications.
He reported that the interfacial temperature and
dwell time are to be the primary factors in controlling heat-seal strength. Pressure normal to the seal
surface had little effect above the level required to
flatten the web for good contact. Stehling and
Meka3,4 had done a series of studies concerning
heat-sealing process. The effect of heat-sealing process variables (seal bar temperature, dwell time, and
pressure) on seal properties (seal strength, seal elongation, and seal energy) of polyethylene films was
quantitatively determined. Their study also shows
that to obtain the highest possible seal strength for a
given semicrystalline polymer, the required platen
temperature can be estimated with the given dwell
time and interfacial temperature by finite element
model. Their results agree with Theller,2 where heatseal strength is primarily controlled by sealing temperature and dwell time, rather than pressure. They
had also established the seal strength versus platen
temperature plot. Several important heat-sealing
quantities such as seal initiation temperature, plateau
initiation temperature, final plateau temperature,
and plateau seal strength are identified in the plot.
Tsujii et al.5 had investigated the effect of heat-sealing temperature on the mechanical properties and
morphology of oriented polypropylene (OPP)/cast
polypropylene (CPP) laminated films. They reported
that tensile strength of the seal was affected by the
orientation of the films. While Yasuo et al.6 had carried out investigation on the failure criteria of the
heat-sealed part of OPP and CPP heat seals made by
impulse type heat-sealing machine. They reported
that seals were stronger in the transverse direction
when compared with the machine direction. Studies
of the effect of corona-discharge treatment (CDT)
on heat-seal strength was done by Owens7 and
Farley and Meka.8 The former has reported that
3737
corona-treated polyethylene films exhibit strong selfadhesion when joined together under conditions of
heat and pressure that give no adhesion with
untreated films. While, the latter found that the primary effect of CDT on the heat-sealing behavior of
LLDPE films is a transition in the failure mode of
heat-seals from a normal tearing or inseparable bond
to a peelable seal. They also found that CDT
increases the seal initiation temperature by 5–178C
and decreases the plateau seal strength by 5–20% as
the treat level, or wetting tension, increases from 31
to 56 dyn/cm. The effect of material type on heatseal strength was reported by Falla9 and Halle and
Davis.10 The earlier reported that the coextruded
films having a heat-seal layer comprised of the ultra
low density polyethylene (ULDPE) resins in the sealing layer of a coextruded film significantly increase
the heat-seal/hot tack range. The ULDPE resin provides broader sealing range for pouch conversion
and better physical properties in finished pouches.
And the latter have shown that to obtain excellent
heat-sealing performance from unlike seal layers is
possible by utilizing a unique family of linear ethylene plastomers.
In this study, the heat sealability of laminated
films using linear low density polyethylene (LLDPE)
and low density polyethylene (LDPE) as the sealant
material are investigated. The effects of various combination of platen temperature and dwell time to the
process window of the laminated films are also studied in view of to provide a guideline for the bar sealing user when setting up their form/fill/seal
machine.
EXPERIMENTAL
Laminated films
Three samples were used in this study, which are
commercial laminated films of various constructions,
thickness, and sealant material uses in flexible packaging application. In Samples 1 and 2, LLDPE is
used as the sealant material, whereas Sample 3 using
LDPE. Details on laminated film description are
summarized in Table I.
Samples 1 and 2 are manufactured from monolayer films using the dry-bond process. In this technique, a liquid adhesive (urethanes) is applied to
TABLE I
Description of Laminated Films
Laminated film’s
designation
Construction description ‘‘outer layer/inner
layer(s)/sealant material (mm)’’
Overall
thickness (mm)
1
2
3
PET/LLDPE(65)
PET/LDPE/F/PET/LLDPE(50)
OPP/LDPE/F/LDPE(20)
79
99
59
Journal of Applied Polymer Science DOI 10.1002/app
3738
YUAN ET AL.
TABLE II
Melting Point of Sealant Materials Determined
Using DSC
Sealant materials
Material forms
Melting point (8C)
LLDPE
LDPE
Monolayer film
Pellet
104.6
88.9
to simulate the most commonly practiced actual
industrial condition, whereas platen temperature
and dwell time varies. After the heat-seal was made,
the sandwich structure was allowed to cool at ambient condition.
Testing of heat-seals
one substrate. It is then dried with hot air. The dried
surface is then adhered to a second substrate using
heat and pressure. Sample 3 was manufactured
using extrusion lamination process. In this process, a
thin layer of LDPE was used to bond together two
layers of film and foil.
Melting point distribution
In this study, Perkin–Elmer differential scanning calorimeter, model DSC-7, was used to study the melting point Tm of the sealing materials. Samples (aged
at room temperature for at least 7 days) of 6 6 4 mg
were prepared and placed in standard aluminum
pans, respectively. The samples were scanned at
108C/min scan rate starting at 25–3008C under a helium purge gas. Results are summarized in Table II.
Heat flow rate of bar sealing process
The rate of heat conduction Q through a plane layer
is proportional to the temperature difference across
the layer DT and measured thermal conductance C
of the laminated film (Lees’ Disc Apparatus). That is,
Heat flow rate, Q ¼ CDT
(1)
After the heat-seals were produced, it was allowed
to condition at room temperature for at least 40 h to
achieve chemical stabilization. Aging of heat-seal
was necessary as the strength of seal may change in
time, which may be due to the memory of polymer,
or thermophysical properties of polymer as the heatseal samples undergo melting and cooling processes.
In practice, packaging goods are aged through storage before distribution. Thus, heat-seals made in this
study were aged for at least 40 h before tested.
The samples were then peeled apart at room temperature in tensile tester of model MICRO 350, using
a 100 N load cell. Each leg of the test specimen was
clamped in the tensile tester. The heat-seal area of
the specimen are placed at approximately equidistant between the clamps. The specimen is aligned
in the clamps so that the seal line is perpendicular to
the direction of pull (as shown in Fig. 2). The constant rate of loading 300 mm/min with initial jaws
separation of 25 mm was chosen as recommended
by ASTM F88–85. The maximum force required to
tear apart the seal, and failure mode of each pull
were recorded.
RESULTS AND DISCUSSION
Heat-seal strength and failure modes
Making of heat-seals
In this project, samples in strip form are prepared
for sealing, in which the sealant material was sealed
together in the interface to simulate the fin seal form
in practice as schematically shown in Figure 1. Laminated films are first cut into 15-mm wide strips by
Lorentzen and Wettre cutter, made in Sweden. This
cutter ensured that clean-cut edges are produced to
prevent premature failures in T-peel test.
Heat-seals were made in the laboratory using a
model HSG/ETK heat-sealer, made in Germany.
This device clamps two pieces of filmstrips between
flat, 10-mm wide heated metal bars. The temperature, pressure, and dwell time of the sealing bars are
adjustable. Microprocessor-programmed controllers
maintained and digitally indicated set temperature
for each bar. Both bars were operated at the same
temperature in these experiments, and kept closed
between sealing to minimize heat loss and temperature fluctuations. The pressure was fixed at two bars
Journal of Applied Polymer Science DOI 10.1002/app
The peeling test measures the forces required to separate a heat-seal after it is allowed to cool. The maximum force per width value obtained in such a test
is commonly defined to be the heat-seal strength. All
representative values in this article are the average
Figure 1 Fin seal dimensions.
HEAT SEALABILITY OF LAMINATED FILMS WITH LLDPE, LDPE
Figure 2
Direction of pull are 908 to the seal in peeling test.
3739
increased of thermal motion (micro-Brownian
movement) of chain segments with temperature,4
and therefore, deepen the original zone of diffusion and causes a greater peeling force required
to peel it apart.
At temperature a few degree Celsius before the
final melting point, seal strength increased
sharply. Sample failed in either peeling, delaminating, or tearing mode. Samples may also fail
with the combination of delaminating and tearing
modes failure. This is the transition region in
which failure mode was then changed from peeling to delaminating or tearing mode failure, or
combination of both failure modes. Acceptable
heat-seal strength was achieved at this stage.
Heat-seal made at temperature substantially
lower than the melting point of the sealant material was found to fail in peeling mode failure.
Under this failure mode, disentangles and extricates chain ends from the opposite surface
occurred, in which the heat-seal bond was peeled
apart (Fig. 3). This happened when the strength
of the seal is lower than the strength of the laminate structures. Hence, heat-seal strength of all
samples reported under this failure mode are
lower than the strengths reported in other failure
modes.
The strength of heat-seal increased gradually
with sealing temperature. This is attributed to the
When sealing was done at plateau initiation temperature or greater, all heat-seals are found to have
failed under delaminating (Fig. 4) or tearing mode
failure (Fig. 5), or combination of both failure modes
(Fig. 6). Delaminating mode failure involves tensile
break of the heat-seal layer, which is thin and weak,
followed by separation of the interlaminar bond.
While, tearing mode failure was due to the weakening of the seal at its edge as the material fused, or
the weakening of the laminate structures as a result
of interlaminar bond separation, plus the geometry
of the peel test itself.
After the acceptable seal strength was achieved,
no significant increase of seal strength with temperature were found for Sample 3. In contrast, the
strength of the seal for Samples 1 and 2 continue to
increase gradually with sealing temperature.
The continuously increase of heat-seal strength in
Samples 1 and 2 may be due to the decrease of amorphousness in the LLDPE film. This is because, higher
temperature setting deepen the molecular entanglement between polymer molecules. Consequently,
Figure 3 Sealing layer torn apart from each other.
Figure 4 The laminated film separated from the sealing
layer.
of six. In addition, failure modes at each pulled was
carefully examined.
Similar to the results reported by previous
researchers,2,4–6 the heat-seal failure of the laminated
films was found greatly influenced by its sealing
temperature and can be discussed in three stages as
following:
Journal of Applied Polymer Science DOI 10.1002/app
3740
Figure 5 Breaking of the laminated film just at the edge
of the seal.
LLDPE chain segments become closely packed, yielding a higher degree of crystallinity in the molecular
structure. Therefore, higher strength is obtained since
polymer with higher crystallinity offer greater physical strength.11
Failure modes of heat-seal had a close relationship
with its strength. As mentioned above, heat-seal
failed in peeling mode failure having relatively
lower strength due to only a slight molecular entanglement between polymer molecules in the interfacial zone. Therefore, heat-seal can easily be peeled
apart before any failure occur to the laminate structures which are relatively stronger than the heat-seal
with only slight molecular entanglement.
As platen temperature increased, deeper molecular
entanglement between polymer molecules in the
interfacial zone occurred. Thus, the heat-seal
strength increased subsequently as the depth of molecular entanglement increased.
Up to a certain level, when the strength of the
heat-seal exceeded the strength of the interlaminar
bond, the laminate structures separated from the
sealing layer instead of peeling of the heat-seal, and
leaving that portion and the other laminated film
intact (Fig. 4). Hence, heat-seal strength reported in
delaminating mode failure was relatively higher
than the heat-seal strength reported in peeling mode
failure.
Figure 6 Combination of delaminating and tearing modes.
Journal of Applied Polymer Science DOI 10.1002/app
YUAN ET AL.
In addition to the increase of heat-seal strength,
the increase of platen temperature also increased the
strength of the interlaminar bond. However, under
marginal condition, uneven strengthening of interlaminar bond on heat-seal area occurred. Laminated
films tested failed in the combination of delaminating and tearing modes failure. In these failure
modes, the laminated film was first separated into
monolayer structures at the peel line. When come to
the area in which uneven strengthening of interlaminar bond occurred, the monolayer structure broke
simultaneously after delaminating, due to the
uneven tensile stress distribution (Fig. 6) at the heatseal area.
When heat-seals are made at a higher platen temperature after obtaining the combine failure modes,
the strength of the interlaminar bond has been
strengthened evenly at the heat-seal area. Laminated
film tested was then failed in tearing mode failure.
This is because the strength of the laminate structures (monolayer films) are now relatively lower
than the strength of the interlaminar bond and the
heat-seal. Under this failure mode, the laminated
film broke just at the edge of the heat-seal (Fig. 5).
Heat-seal strength achieved under this failure mode
is the highest when compared with heat-seal
strength reported under other failure modes.
Effect of platen temperature and dwell time
Figure 7 shows the effects of dwell time on heat-seal
strength at different platen temperature for Sample
1. At temperatures substantially lower than the melting point of the sealant material, no effects of dwell
time on heat-seal strength is observed. The lowest
activated temperature of this sample was 1128C. As
may be seen, heat-seal strength changes with dwell
time at this temperature setting. For instance, the
heat-seal strength increased from 0.13 to 1.86 N/mm
when sealed with dwell time setting of 0.1 and 1 s,
respectively. This was due to the transient change in
the interfacial temperature with time. After 1 s, no
effect of dwell time on heat-seal strength was
Figure 7 Graph of heat-seal strength versus dwell time at
various platen temperatures for Sample 1.
HEAT SEALABILITY OF LAMINATED FILMS WITH LLDPE, LDPE
Figure 8 Graph of heat-seal strength versus dwell time at
various platen temperatures for Sample 2.
detected, because the steady-state interfacial temperature had been achieved.
At relatively higher platen temperature, the effect
of dwell time on heat-seal strength was even greater.
For example, at 1158C, 0.2 s was required to achieve
an acceptable heat-seal strength. However, this can
be achieved at 0.1 s when sealing is made at 1188C
or higher.
Similar results are reported for Sample 2. As may
be seen in Figure 8, acceptable heat-seal strength
was achieved at 0.4 s, when sealed at lowest activated temperature of 1188C. However, this can be
achieved at a faster speed when sealing was made at
a higher temperature setting.
Notable that the heat-seal strength of all sample
were slightly decreased at all temperature setting when
sealed at 1 s or longer. This may due to the weakening
of the seals as it had been pressed in between the
heated bar at the molten state, which reduces the thickness of the seals. This may also be caused by the
decrease of material properties when exposed to temperature at a relatively longer period of time. The
decrease of heat-seal strength may not be significant
though, it is however, recommended that the dwell
time should not be set longer than 1 s as this will bring
no beneficial effect on the heat-seal strength.
The study of heat-seal strength beyond 1 s of
dwell time is only of theoretical interest. In practice,
the setting of dwell time will not be longer than 1 s
as most of the packaging machine is operating at
very high speed.
Figure 9 shows the effect of heat-seal strength on
dwell time at various platen temperatures for Sample 3. As shown in the graph, heat-seal strength was
dependent mainly on platen temperature. No
increase of heat-seal strength with dwell time was
detected. This is because the relatively higher thermal conductance of the sample allowed the seal to
be made at shorter dwell time.
Previous researchers have also confirmed that the
main factors affecting heat-seal strength is the platen
temperature. The results of Theller,2 who looked at the
3741
Figure 9 Graph of heat-sealing strength versus dwell
time at various platen temperatures for Sample 3.
effect of dwell time at constant platen temperature,
indicated that the heat-seal strength is a strong function of platen temperature and is not dependent on
dwell time beyond 0.4 s for LDPE film sealed at 106
and 1108C. In addition, Yasuo6 stated that tensile failure which occurred inside the heat-seal is more sensitive to sealing temperature. Meka and Stehling3 also
reported that heat-seal strength depends primarily on
plated temperature and secondary on dwell time.
Effect of platen pressure
Meka and Stehling3 reported that platen pressure
has no measurable effect on heat-seal strength. Only
a small level of pressure was required to bring the
surface into contact. In this study, the effect of platen
pressure on heat-seal strength was investigated on
Sample 1. The platen temperature of 1138C was
used. As may be seen in Figure 10, no significant
change of heat-seal strength with platen pressure
was found. These confirmed the results reported by
the previous researchers.
Heat-sealing curve
Heat-seal strength versus platen temperature curves at
dwell time setting of 1 s are shown in Figure 11. The
heat-sealing curves for all samples were found having
Figure 10 Graph of heat-seal strength versus sealing pressure for Sample 1.
Journal of Applied Polymer Science DOI 10.1002/app
3742
YUAN ET AL.
Sample 3 that used LDPE as the sealant material
required Tpi to be set 188C higher then the Tmf,
whereas, Samples 1 and 2, which use LLDPE as the
sealing material, Tpi required to be set about 108C
higher then the Tmf.
Thermal conductance
Thermal conductance of each sample was measured
using the Lees’ Disc Apparatus method. Results in
Table III shows that Sample 3 have the highest thermal conductance, followed by Sample 1 the middle
and Sample 2 the lowest.
Figure 11 Graph of heat-seal strength versus platen temperature at dwell time of 1 s.
a similar shape to that of the idealized heat-seal
strength curve established by Stehling and Meka.4
Heat-sealing curve obtained on Samples 1 and 2
exhibited slightly different with continuously
increase of heat-seal strength after the acceptable
heat-seal was achieved. Therefore, no plateau region
reported as plateau seal strength is defined to be the
strength when reaches a constant value.
As shown in Figure 11, heat-seal began to be
made at a temperature which was found substantially lower then the melting point of the sealing
materials. This temperature is called seal initiation
temperature, where a measurable but low level of
seal strength was achieved.
As platen temperature increased, seal strength
increased gradually. At temperature a few degree
Celsius before plateau initiation temperature, seal
strength increased greatly for Samples 1 and 2. Contrary, Sample 3 exhibited only little increase of its
seal strength. This is attributed to the low achievable
plateau seal strength in Sample 3 that is made by
extrusion lamination process. The reason is, in extrusion lamination process, LDPE was used to bond together other substances. However, the intrinsic adhesive affinity of LDPE (adhesive agent of extrusion
lamination process) toward other substance is limited.1 Therefore, laminated films made by extrusion
lamination process, such as Sample 3, have relatively
low level of achievable plateau seal strength.
Heat flow rate
As defined in eq. (1), heat flow rate for conduction
state at steady flow condition is proportional to the
conductance of laminated films and heat force of the
process. Assuming the outer surface temperature of
the laminated film rise to the thermal condition of
platen temperature at the moment of contact, and is
kept at this thermal condition while the interfacial
temperature are at room temperature during heatsealing cycle, and steady heat flow condition
occurred, the heat flow rate calculated using eq. (1)
for each sample at the plateau initiation temperature
setting were as shown in Table IV.
Graph of heat flow rate versus dwell time at the
lowest activated temperature (Fig. 13) shows that
the dwell time of heat-sealing process corresponds
closely with the heat flow rate of the laminated
films. Samples with greater heat flow rate were
sealed with shorter dwell time because heat flow
was faster in those samples.
Plateau initiation temperature
For all samples, the temperature where the plateau
begins (Tpi) corresponds closely to the final melting
point (Tmf) of their sealant materials. This was shown
in Figure 12, where the Tpi is plotted against Tmf for
both samples. The straight line in this figure is the
locus Tpi ¼ Tmf, and all points fall closely to this
locus.
Journal of Applied Polymer Science DOI 10.1002/app
Figure 12 Graph of plateau initiation temperature versus
final melting point.
HEAT SEALABILITY OF LAMINATED FILMS WITH LLDPE, LDPE
3743
TABLE III
Thermal Conductance of Laminated Films Determined
Using Lees’ Disc Apparatus
Sealant materials
LLDPE
LDPE
Material forms
Melting point (8C)
Monolayer film
Pellet
104.6
88.9
Because heat flow rate is directly proportional to
platen temperature and thermal conductance of the
laminated film, thus in the case when the use of longer dwell time is not permissible, a higher platen
temperature setting can be used to achieve the same
flow rate. This is evident in Samples 1 and 2, where
Tpi setting for Sample 2 was 38C higher than Sample
1 when sealed at the same dwell time.
However, it is recommended that laminated films
with higher thermal conductance is preferable as it
allowed the use of shorter dwell time and lower
platen temperature setting. The former have direct
impact on the production speed and the latter have
less harmful effect on the product and uses lower
energy in a long run.
Process windows of bar sealing application
Figure 14 shows the general process window of bar
sealing application. The process window can be
approximately described by several quantities illustrated in the figure:
1. The left vertical border, this border indicated
the shortest dwell time, which was determined
by the minimum possible time setting of the
sealing machine. However, this do not limits
the practical usage of the process window as
almost all the machines having the same limit
of 0.1 s, and dwell time required in commercial
production rate is commonly longer than 0.1 s.
2. The right vertical border, this border indicated
the longest dwell time suggested in the process
window. Longest dwell time of 1 s was selected
because all samples exhibited approximately
constant value or slight decrease of the heatseal strength after 1 s dwell time (Figs. 7–9). In
practice, dwell time required for commercial
production rate is usually at the setting of 0.3–
Figure 13 Graph of heat flow rate versus dwell time at
lowest activated temperature.
0.7 s. Hence, 1 s of longest dwell time in the
window is sufficient to provide adequate reference for practical usage.
3. The lower border, the lowest activated platen
temperature setting for each particular dwell time
is revealed in the lower border. Setting fall on
this border is the optimum combination of platen
temperature and dwell time, because no excessive temperature was used under this setting.
4. The upper horizontal border, heat-seal can be
made in a rage of platen temperature setting,
however, lower sealing temperature uses less
energy, allow the package to be handle quicker,
and have less potential effect on the contained
product.11 Therefore, higher platen temperature
of 158C after the lowest activated temperature
setting is selected to be the highest temperature limit of the window. Combination of platen
temperature and dwell time after the highest
temperature limit is not recommended because
it is not efficient.
Figures 15–17 show the process windows of Samples
1–3 respectively. All points drop inside the window
are combination of platen temperature and dwell time
that produced acceptable heat-seal. Points drop on the
lower borderline were optimum combination of platen
TABLE IV
Heat Flow Rate Calculated at the Plateau Initiation Temperature
Laminated film
designation
1
2
3
Construction description ‘‘outer layer/inner
layer(s)/sealant material (mm)’’
PET/LLDPE(65)
PET/LDPE/FOIL/PET/LLDPE(50)
OPP/LDPE/FOIL/LDPE(20)
Heat flow rate
(1 105 W/m2)
1.257
1.321
1.367
Journal of Applied Polymer Science DOI 10.1002/app
3744
YUAN ET AL.
Figure 14 General process window of bar sealing application.
temperature and dwell time, because no excessive
temperature was used.
In many cases, a form/fill/seal machine used to
produce the heat-seal packages was set to run at a
desired production speed, and so dwell time is virtually a given. Hence, process window become a
very helpful guide to provide information about
which platen temperature to be used to produce an
acceptable heat-seal at the optimum condition. For
example, suppose Sample 2 is to be used, and the
machine is to be run at the dwell time setting of
0.3 s, the optimum platen temperature setting would
then be at 1218C (Fig. 16). However, in some cases,
high production rate is not required which might be
due to a lower market demand of the products.
Thus the machine is designed to run at lower speed
incorporated with a longer dwell time. In that case,
Figure 15
Process window of Sample 1 at 2 bar.
Journal of Applied Polymer Science DOI 10.1002/app
Figure 16 Process window of Sample 2 at 2 bar.
the combination of 0.5 s dwell time and 1188C platen
temperature can certainly reduce the energy consumption by the entire process as lower temperature
setting is used.
As illustrated in the bar sealing process windows
(Figs. 15–17), a very short dwell time of 0.1 s can be
used while combined with a very high temperature.
However, care should be taken while selecting the
material for the outer construction of the laminated
film, because the outer surface of the laminated film
would be contacted directly to the heated bar. Therefore, materials of higher melting point should be
considered to avoid damage of the seal area, which
can occur if the heated bar temperature exceed the
melting temperature of the material of the outer construction.
Figure 17
Process window of Sample 3 at 2 bar.
HEAT SEALABILITY OF LAMINATED FILMS WITH LLDPE, LDPE
For process window of Sample 3, the lower border
of the process windows was form by a horizontal
line. This indicated that the acceptable heat-seal
could be obtained at any dwell time setting for as
long as the activated temperature level has been
achieved. As discussed above, shorter dwell time
can be used when higher heat flow rate is provided.
But unlike other samples, the very short dwell time
of 0.1 s can be used at the lowest activated temperature setting for this sample was attributed to its very
good thermal conductance. Therefore, laminated
films having higher thermal conductance provide
better combination of plated temperature and dwell
time, which helps to reduce energy consumption
in the heat-sealing process, by allowing lower platen
temperature setting even though a very short dwell
time is used.
GENERAL CONCLUSIONS
The main conclusions that can be derived from the
study are as follows:
1. Bar sealing process window for each samples
were developed. Information about the optimum combination of platen temperature and
dwell time for each individual laminated film
can be obtained in the respective process windows. Thus, optimum machine setting can be
predicted when the laminated films are to be
used in the real application and machine setting
time can be reduced.
2. The effect of bar sealing process variables on
heat-seal strength of laminated film has been
quantitatively determined. Heat-seal strength
was determined primarily by the platen temperature, and secondly by dwell time. Higher
platen temperature was required to seal laminated film having lower thermal conductance.
However, shorter dwell time was required if
the increase of the platen temperature had
increased the heat flow rate of the process.
Dwell times of the order of 0.3–0.5 s required
for commercial productions rates can be
obtained by proper selection of the individual
plated temperature. The heat-seal strength is
not significantly affected by pressure. However,
3745
some level of pressure is necessary to bring two
heated laminated films into intimate contact to
effect sealing.
3. The achievable heat-seal strength was also
determined by the lamination process used to
produce the laminated film, and sealant material used in the laminated film. Laminated films
made from extrusion lamination process provide lower achievable heat-seal strength when
compared with the laminated films made from
dry-bond lamination process.
4. Platen initiation temperature closely corresponds to the final melting point of the sealant
materials. To achieve plateau seal strength,
laminated films using LDPE and LLDPE as
sealant materials required platen temperature to
be set slightly higher than the final melting
point of the sealant materials. Outer construction with higher melting temperature was preferable for laminated film that required to be
sealed using higher platen temperature to avoid
damage on the outer seal area.
5. Strength of heat-seal and its failure modes are
closely related. Heat-seal strength achieved
under tearing mode failure is the highest, followed by heat-seal strength achieved under
delaminating mode failure, and the heat-seal
strength achieved under peeling mode failure is
the lowest.
References
1. Brody, A. L.; Marsh, K. S, Eds. The Wiley Encyclopedia of
Packaging Technology, 2nd ed.; Wiley: United State of America, 1997, p 823.
2. Theller, H. W. J Plast Film Sheeting 1989, 5, 66.
3. Stehling, F. C.; Meka, P. J Appl Polym Sci 1994, 51, 89.
4. Stehling, F. C.; Meka, P. J Appl Polym Sci 1994, 51, 105.
5. Tsujii, T.; Tetsuya, T.; Ishiakw, U. S.; Mizoguchi, M.; Hamada,
H. J Appl Polym Sci 2005, 97, 753.
6. Yasuo, H.; Hashimoto, Y.; Ishiakw, U. S.; Leong, Y. W.; Hiroyuki,
H.; Tsujü, T. Polym Eng Sci 2005, 46, 205.
7. Owens, D. K. J Appl Polym Sci 1975, 19, 265.
8. Farley, J. M.; Meka, P. J Appl Polym Sci 1994, 51, 121.
9. Falla, D. J. The use of ULDPE’s in pouch for packaging flowable materials. SPE ANTEC 1994, III, 3141.
10. Halle, R. W.; Davis, D. S. Heat sealing linear ethylene plastomers to ionomers or LLDPEs. SPE ANTEC 1995, 1, 2.
11. Soroka, W, Ed. Fundamentals of Packaging Technology; Institute of Packaging Press: Virginia, 1998. p 313.
Journal of Applied Polymer Science DOI 10.1002/app
View publication stats